The present invention is directed to a liquid starch phosphate adhesive composition comprising a selected phosphorylated starch material prepared by steam injection cooking at high temperature and pressure. This starch phosphate composition is a natural adhesive material which is viscosity stable over time and possesses suitable rheological properties making it especially useful as an adhesive in the manufacture of cigarettes.
Cigarettes are generally comprised of a cigarette rod and most often a filter or plug. The cigarette rod consists of a stream of tobacco wrapped in a paper tube, the paper tube being glued along one longitudinal edge with a suitable adhesive (side seam or lap seal). The filter or filter plug generally consists of a crimped textile tow of cellulose acetate fibers treated with a plasticizer and wrapped into a cylindrical form with paper. The center of the paper is attached to the fibers using an adhesive (center-line adhesive) and the paper is then wrapped around the plug rod, overlapping and attaching itself with an adhesive (overlap adhesive) to form the cylindrical filter plug. The filter or plug is then attached to the cigarette rod by wrapping another paper (tipping paper) which contains an adhesive (tipping adhesive) around the plug and overlapping it with an aligned rod.
Most cigarette manufacturing processes involve high speed operations (2000-12000 cigarettes per minute) where the adhesive is typically applied by nozzle (side seaming, center-line and overlap), paste wheel (side seaming) and by rollers (filter tipping). Adhesives used in these operations are generally synthetic emulsions but because of increasing interest and tobacco regulation requirements in different countries, natural type adhesives are being sought to replace the synthetics.
Starch has long been used as an adhesive material in various applications such as case and carton sealing, laminating, tube winding, papermaking, etc., as described in Starch: Chemistry and Technology, Second Edition by R. Whistler, J. Bemiller and E. Paschall, 1984, pp. 593-610. Dextrins and thin-boiling starches are disclosed as useful as side seam adhesives but generally at lower solids than being required at current high speed manufacturing operations.
Starch phosphates prepared by phosphorylation reactions of starch, wherein starch is impregnated with a phosphate salt and thereafter dried and heat-reacted are well known in the art, as described in Modified Starches: Properties and Uses, edited by O. B. Wurzburg, 1986, pp. 97-112. U.S. Pat. No. 3,642,774 discloses phosphorylating of starch to form starch phosphates, viz: low molecular weight, highly water soluble dextrin phosphates and further describes various uses for these compositions including for the surface sizing and coating of paper and as adhesives. U.S. Pat. No. 3,637,407 discloses a similar dextrin phosphate composition containing a small proportion of ketene dimer, the composition being especially useful in surface sizing paper.
The cooking of starch at high temperature and pressure in continuous operations is well known as disclosed in Whistler noted above and on pages 555-557. One such method disclosed in Japanese Patent No. 57-11579, published Mar. 5, 1982, involves continuous adhesive manufacturing of natural or synthetic adhesive materials using high pressure heating and forced stirring. Other methods are disclosed in U.S. Pat. Nos. 2,582,198; 3,424,613 and 4,256,771.
However, despite continued developments and improvements for adhesive properties and technological advances in the manufacturing techniques for producing adhesives, there still is the need for a natural adhesive material which will satisfy the requirements of current cigarette production. This has not been easy to accomplish particularly because of the demanding high speed operation and the required properties that adhesive materials used in these operations must possess including flow or fluidity, drying speed, cohesiveness, bonding strength, viscosity stability, humidity resistance, machinability and other rheological characteristics.